Plasterboard composition, preparation of this composition and manufacture of plasterboards

ABSTRACT

A plasterboard composition includes from 55 to 92% of hydratable calcium sulphate; from 0.1 to 5% of mineral and/or refractory fibres; from 3 to 25% of a mineral additive; from 1 to 5% of unexpanded vermiculite; and from 3 to 15% of hydrated alumina.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application is a continuation of PCT International Application No. PCT/FR01/02125, filed in France on Jul. 3, 2001, which claims the priority of French Patent Application No. 00 09 392, filed in France on Jul. 18, 2000, the entire contents of both applications are hereby incorporated herein by reference.

BACKGROUND OF THE APPLICATION

[0002] The present invention relates to a plasterboard composition, a method of preparing this composition and a process for manufacturing plasterboards having a greatly improved fire resistance.

[0003] It is well known to use plasterboards for producing partitions, coverings of vertical or inclined elements, or for producing ceilings, whether suspended or not.

[0004] These boards generally consist of a core, essentially made of plaster, covered on each of its sides with a sheet which serves both as reinforcement and as facing and which may be made of paperboard or of mats of mineral fibres.

[0005] U.S. Pat. No. 3,616,173 describes a fire-resistant board of low density (between 0.64 and 0.8 g/cm³), the core of which is based on plaster, glass fibres, a mixture or not, of clay, colloidal silica and/or colloidal aluminium oxide, and optionally of unexpanded vermiculite.

[0006] In that patent, it is specified that silicon and aluminium oxides, in dry powder form, are difficult to disperse and also expensive. For this reason in particular, that patent recommends the use of clays. The plasterboard according to that patent has a high-temperature shrinkage, which is quite low, but its fire resistance is limited. Such a board therefore does not have the properties needed to constitute good fire protection.

[0007] European Patent Application No. 0 470 914 of the Applicant disclosed in 1992 a plasterboard intended for fire protection, the faces of which are covered with a reinforcing material based on yarns and/or fibres of a mineral and/or refractory material. The core of this boards comprises:

[0008] 55 to 94% of plaster;

[0009] 0.1 to 5% of mineral and/or refractory fibres;

[0010] 2 to 25% of silica;

[0011] 1 to 15% of talc and/or mica; and

[0012] optionally, aluminium hydroxide and/or expanded vermiculite.

[0013] Since then, the Applicant has continued its research in the field of plasterboards with a view to improving both the hot mechanical strength, the shrinkage behaviour and the heat transfer of its plasterboards.

[0014] It has now achieved its objectives by developing a plasterboard composition comprising:

[0015] from 55 to 92% of hydratable calcium sulphate;

[0016] from 0.1 to 5% of mineral and/or refractory fibres;

[0017] from 3 to 25% of a mineral additive;

[0018] from 1 to 5% of unexpanded vermiculite; and

[0019] from 3 to 15% of hydrated alumina.

[0020] According to a preferred embodiment of the invention, the nature and the amount of mineral additive are chosen so that the plasterboard composition contains at most 2% crystalline silica and/or at most 1% cellular crystalline silica, that is to say silica having crystals of less than 5 microns in size. Such a composition therefore has the advantage of having a crystalline, especially cellular, silica content in accordance with the recommendations of the International Agency for Research on Cancer, according to which it is recommended to reduce the use of cellular crystalline silica as far as possible since this compound is assumed to have a maximum toxicity.

[0021] The second subject of the invention is a method of preparing a plasterboard composition, in which the constituents of the plasterboard composition defined above are mixed in any order.

[0022] Finally, the third subject of the invention is a continuous process for manufacturing plasterboards, essentially comprising the following steps:

[0023] preparation of a slurry by mixing the various constituents of the composition with water in a mixer;

[0024] deposition of the slurry thus prepared on the reinforcing material, followed by shaping and covering of the upper face of the slurry using a second reinforcing material;

[0025] where appropriate, shaping of the edges of the board obtained previously by moulding the fresh board on profiled bands, this forming consisting especially in tapering the edges of the board;

[0026] hydraulic setting of the hydratable calcium sulphate on a manufacturing line while the ribbon of hydratable calcium sulphate board runs along a conveyor belt;

[0027] cutting of the ribbon at the end of the line into predetermined lengths; and;

[0028] drying of the boards obtained.

[0029] Further characteristics and advantages of the invention will now be described in detail in the description, which follows and is given with reference to the drawings in which:

[0030]FIG. 1 shows the variation in shrinkage as a function of time for the control board and boards A and B;

[0031]FIG. 2 shows the variation in the shrinkage as a function of time for the control board and the boards B, C and D during another test;

[0032]FIG. 3 shows the temperature rise on the unexposed side of the control plasterboard and plasterboards A and B;

[0033]FIG. 4 shows the temperature rise on the unexposed side of the control plasterboard and plasterboards B and C, during another test; and

[0034]FIG. 5 shows the temperature rise on the unexposed side of the control plasterboard and plasterboard D during another test.

[0035] The subject of the invention is therefore a plasterboard composition that can be used to manufacture a plasterboard having a greatly improved fire resistance.

[0036] This composition comprises (in % with respect to the entire dry mix)

[0037] from 55 to 92% of hydratable calcium sulphate;

[0038] from 0.1 to 5% of mineral and/or refractory fibres;

[0039] from 3 to 25% of a mineral additive;

[0040] from 1 to 5% of unexpanded vermiculite; and

[0041] from 3 to 15% of hydrated alumina.

[0042] The term “hydratable calcium sulphate” should be understood to mean, within the present context, an anhydrous calcium sulphate (anhydrite II or III) or a semihydrated calcium sulphate (CaSO₄×½H₂O) in its a or b crystalline form. Such compounds are well known to those skilled in the art and are generally obtained by baking a gypsum.

[0043] The mineral and/or refractory fibres are preferably glass fibres. They may be short (3 to 6 mm on average) or else long (10 to 24 mm on average) or of intermediate lengths. Preferably, glass fibres having a single length of 13mm ±5 mm are used.

[0044] In particular, fibres coming from an E-type glass are used, these possibly being in two forms, one being in a form called a “roving” comprising glass strands supplied on reels and cut before they are introduced into the usual circuit for mixing the hydratable calcium sulphate with water, or else in the form of precut strands which are metered before mixing the hydratable calcium sulphate with water.

[0045] Preferably, fibres having a length of about 13 mm (±5 mm) and a diameter of about 13 microns (±5 μm) are used.

[0046] The essential function of the glass fibres is to impart high-temperature mechanical strength, allowing the cohesion of the calcined plaster to be maintained.

[0047] As mineral additive, numerous clays may be used. The advantages afforded by clays are, on the one hand, the fact that they release the water that they contain (water of constitution) when they are heated to a temperature between 100 and 600° C. and, on the other hand, the fact that they compensate for the shrinkage of the plaster in a fire because of their ability to exfoliate.

[0048] Preferably, the nature and the amount of mineral additive are chosen so that the plaster composition contains at most 2% crystalline silica and/or at most 1 % cellular crystalline silica.

[0049] It is therefore advantageous to use a mineral additive comprising at most 7.5% of cellular crystalline silica.

[0050] As mineral additive, it is possible to use a mineral additive comprising essentially a clayey material, the amount of crystalline silica of which is at most equal to about 15% by weight of the mineral additive, and an inert mineral supplement compatible with the clayey material and dispersible in the hardened plaster substrate.

[0051] For example, it is possible to use a mineral additive comprising, as clayey material, kaolin, illite, quartz and, as mineral supplement, dolomite. In particular, a mineral additive is used which has the following composition (in percentages by weight with respect to the total weight of mineral additive):

[0052] 25% of kaolin;

[0053] 10% of illite;

[0054] 15% of quartz; and

[0055] 50% of dolomite.

[0056] The calcined chemical composition of this additive is the following (in %)

[0057] SiO₂:43

[0058] TiO₂:1.1

[0059] Al₂O₃:15

[0060] Fe₂O₃:1.6

[0061] K₂O:1.2

[0062] CaO:23

[0063] MgO:14

[0064] Its particle size is expressed by a 63 μm screen oversize of less than 15%.

[0065] Its loss on ignition at 900° C. is 26.5%.

[0066] The composition according to the invention comprises unexpanded vermiculite, which is an aluminium-iron-magnesium silicate in the form of flakes, which expand at a temperature above 200° C., thereby making it possible to compensate for the shrinkage of the plaster. Furthermore, the unexpanded vermiculite improves the thermal resistance of the plaster.

[0067] Preferably, a micronized unexpanded vermiculite is used, that is to say one in which all the particles are less than 1 mm in size. This has the advantage of making it possible for the vermiculite to be better distributed within the plaster and of avoiding an abrupt expansion causing structural disorders.

[0068] Hydrated alumina (aluminium trihydroxide) is preferably used with a fine particle size (median diameter of about 10 microns). It has the effect of giving rise to an endothermic reaction complementary to that of gypsum, especially by having a water of crystallization content of about 35%, the water being releasable between 200 and 400° C. (gypsum containing about 20% of water releasable at about 140° C.).

[0069] The composition according to the invention may furthermore possibly include up to 4%, especially from 1 to 4%, of boric acid, as this product advantageously loses its water of constitution above 100° C., thereby contributing to the fire resistance of the plasterboard. Moreover, boric acid modifies the crystalline structure of the hydrated calcium sulphate in a manner favourable as regards shrinkage on ignition.

[0070] The composition according to the invention may be prepared by mixing, per 100 parts by weight of composition:

[0071] from 55 to 92 parts by weight of hydratable calcium sulphate;

[0072] from 0.1 to 5 parts by weight of mineral and/or refractory fibres;

[0073] from 3 to 25 parts by weight of a mineral additive;

[0074] from 1 to 5 parts by weight of unexpanded vermiculite; and

[0075] from 3 to 15 parts by weight of hydrated alumina.

[0076] The manufacture of the plasterboards may be carried out essentially according to the following steps:

[0077] preparation of a slurry by mixing the various constituents of the composition with water;

[0078] deposition of the slurry thus prepared on the reinforcing material, followed by forming and covering of the upper face of the slurry using a second reinforcing material;

[0079] where appropriate, shaping of the edges of the board obtained previously by moulding the fresh board on profiled bands;

[0080] hydraulic setting of the hydratable calcium sulphate on a manufacturing line while the ribbon of hydratable calcium sulphate board runs along a conveyor belt;

[0081] cutting of the ribbon at the end of the line into predetermined lengths; and

[0082] drying of the boards obtained.

[0083] After this treatment, the plasterboards are ready for use.

[0084] According to an embodiment, the density of the hardened composition which constitues the core of the boards is between 800 and 1,000 kg/m³.

[0085] The reinforcing material may be based on mineral or refractory fibres. It may be in the form of a web, a fabric or a mat of mineral fibres, preferably glass fibres. The web, fabric or mat may be combined with a sheet of mineral and/or refractory, entangled continuous yarns or yarn meshes, or in another form.

[0086] The reinforcing material may also be made of cardboard.

[0087] Preferably, a reinforcing material made of glass yarns or fibres is used.

[0088] The plasterboard according to the invention has the following advantages:

[0089] the composition can be easily formulated in the form of a fluid slurry which is then converted, advantageously continuously, into a plasterboard in conventional plants used for this type of manufacture;

[0090] by virtue of the presence of an outer reinforcing material, the edges of the plasterboard may be advantageously shaped, particularly tapered, during manufacture of the board;

[0091] it provides effective fire protection; thus boards according to the invention, having a thickness of around 12.5 mm and a density of around 0.88 g/cm³, guarantee fire resistance for longer than 2 hours;

[0092] by virtue of their good dimensional stability, the boards according to the invention after the fire resistance test maintain a good overall appearance without any deep cracking and exhibit mechanical integrity (this behaviour is important for applications requiring a very high level of fire protection, such as air ducts for ventilation and for smoke venting, in which there is a requirement for them to seal against hot gases under high pressure);

[0093] the results of the reaction-to-fire tests on plasterboards according to the invention are very good: when these boards are exposed to the action of a radiating source and/or a specific burner under defined conditions (for 20 minutes), capable of igniting the gases released and of propagating the combustion, it has been found that there is no ignition and that the deterioration of these boards is merely superficial; after this test, the plasterboards according to the invention are therefore still capable of stopping the spread of a fire;

[0094] because of its lightness and its ability to be worked (cut, nailed, screwed, stapled, screwed/bonded, etc.), it is very easy to install; advantageously, it has tapered edges with which it is possible to produce reliable joints between the boards using plasterboard jointing compounds, for example of the type of those used for plasterboards faced with paperboard, and preferably fire-resistant jointing compounds; in addition, there are various possible ways of finishing off the construction elements produced with boards according to the invention, especially with paint, wallpaper, etc.;

[0095] it has the application characteristics required in the construction field: such as flexural stiffness, high impact strength, moisture resistance and no creep in the presence of moisture or under its own weight when it is mounted as a ceiling; and

[0096] finally, given that it can be manufactured using a simple process well known in the plasterboard field and that, in addition, the raw materials of which it is composed are quite inexpensive, the plasterboard according to the invention has the advantage of having a moderate manufacturing cost.

[0097] The best performance is achieved with boards obtained from the following composition:

[0098] 70 to 80% of a hydratable calcium sulphate semihydrate;

[0099] 1 % of glass fibres

[0100] 10 to 15% of the clay described above, consisting of 25% kaolin,

[0101] 10% illite, 15% quartz and 50% dolomite;

[0102] 2 to 4% of unexpanded micronized vermiculite;

[0103] 6 to 10% of hydrated alumina; and

[0104] 0 to 2% boric acid.

[0105] Of course, provided that the proportions assigned to each of the essential constituents are respected, it is possible to introduce, into the composition according to the invention, by way of secondary ingredients, additives normally used to facilitate the processing of the other constituents or for imparting additional particular properties on the composition. By way of examples of such additives, mention may be made of fluidizing agents, foaming agents, setting accelerators and water-repellent agents.

Examples

[0106] The following examples are given purely by way of illustration and are in no way limiting in character.

Example 1

[0107] A control board was prepared according to the aforementioned European Patent Application No. EP-A-0470914 and four boards A, B, C and D according to the invention.

[0108] The composition of the boards is given in the following table: Composition (%) Control A B C D Plaster 76  76 76 76 74  Glass fibres 1  1  1  1 1 Clay — 18 13 10 13  Vermiculite —  2  4  3 2 Hydrated alumina 10   3  6 10 8 Boric acid — — — — 2 Quartz 9 — — — — Talc 4 — — — —

[0109] The hydratable calcium sulphate used came from the industrial baking of desulphurized gypsum (FGD).

[0110] The clay used consisted of 25% kaolin, 10% illite, 15% quartz and 50% dolomite.

[0111] The vermiculite used was a micronized unexpanded vermiculite.

Example 2

[0112] The hot mechanical strength (also called the high-temperature core cohesion) of the control board and boards A, B, C and D prepared in Example 1 were measured.

[0113] The test used combined a thermal stress, exerted on both sides of the test sample by means of a Mecker burner delivering a flame having a constant temperature of 1020° C., with a tensile mechanical stress of 0.2 kg/cm².

[0114] The parameters recorded were the failure time and the final shrinkage.

[0115] The results are given in the following table: Board Control A B C D Failure time (min) >100 >120 >120 109 93.5 Shrinkage (%) 4.4 2.1 2.95 1.5 1.3

[0116] It may be seen that failure of the control, A and B test specimens was reached after two hours of stressing. Moreover, all the formulations lasted at least 1 hour 30 minutes.

[0117] In the case of all the plasterboard test specimens according to the invention, it may be seen that the combination of micronized unexpanded vermiculite combined with clay allows the final shrinkage to be reduced to less than 3%.

[0118] Test specimen D containing boric acid has the least shrinkage.

Example 3

[0119] The shrinkage behaviour of the control board and boards A, B, C and D prepared in Example 1 was measured.

[0120] The test involved consisted in simply exerting the same thermal stress as in Example 2, in the absence of any mechanical stress.

[0121] The recorded parameter was the shrinkage after 15, 30, 45 and 60 minutes.

[0122] The results are given in the following table: Shrinkage of the boards in % Time (min) Control A B C D 15 3.0 1.3 1.4 0.3 0.9 30 3.0 1.4 1.1 0.5 1.2 45 3.2 1.6 1.7 0.8 1.1 60 3.6 1.5 2.5 1.2 0.7

[0123]FIG. 1 shows the variation in the shrinkage as a function of time for the control board and boards A and B.

[0124]FIG. 2 shows the change in shrinkage as a function of time for the control board and boards B, C and D, during another test.

[0125] The difference between the control and the test specimens according to the invention is very marked, particularly in the initial phase (up to 30 minutes. The micronized unexpanded vermiculite/clay pair reduces the shrinkage by a factor of about 2 compared with the control.

[0126] Again, it is found that the shrinkage is minimal with test specimen D containing boric acid.

Example 4

[0127] The heat transfer of the control board and boards A, B, C and D prepared in Example 1 was measured.

[0128] The test consisted in exerting a thermal stress on one side of the by means of a Mecker burner delivering a flame with a constant temperature of 1020° C.

[0129] The parameters recorded were the temperature of the unexposed test specimen, the time to reach values corresponding to the Fire Wall and insulation classification criterion according to the French Decree of August 1999 and the EN 1361-1 and EN 13 501-2 standards, in which dt=140° C. on average or a maximum of 180° C. at any point.

[0130] In addition, the time to reach a temperature of 400° C. was also recorded, as this time is a significant measure of the heat transfer after dehydration.

[0131] The results are given in the following table: Time(s) to reach temperature Boards Temperature Control A B C D 160° C. 595 525 655 640 570 200° C. 645 615 710 690 635 400° C. 945 930 1035  1105  1020 

[0132]FIG. 3 shows the temperature rise on the unexposed side of the control plasterboard and plasterboards A and B.

[0133]FIG. 4 shows the temperature rise on the unexposed side of the control plasterboard and plasterboards B and C, during another test.

[0134]FIG. 5 shows the temperature rise on the unexposed side of the control plasterboard and plasterboard D, during another test.

[0135] All the tests were carried out under the same conditions.

[0136] It may be seen that the shape of the curves are similar, with a first vaporization plateau around 100° C. and then another one around 120° C.

[0137] Moreover, heat transfer through the calcined board takes place up to a maximum point at 450° C.

[0138] The results on test specimen A are comparable to those on the control test specimen.

[0139] The results of all the other test specimens according to the invention are better than those of the control board, especially both from the standpoint of the duration of the vaporization plateau, thus guaranteeing that a fire-wall criterion is met for a longer time, and reduced heating in the 200 to 400° C. region.

[0140] Although only preferred embodiments are specifically illustrated and described herein, it will be appreciated that many modifications and variations of the present invention are possible in light of the above teachings and within the purview of the appended claims without departing from the spirit and intended scope of the invention. 

What is claimed is:
 1. Plasterboard composition comprising: from 55 to 92% of hydratable calcium sulphate; from 0.1 to 5% of mineral or refractory fibres; from 1 to 5% of unexpanded vermiculite; and from 3 to 15% of hydrated alumina; from 3 to 25% of a mineral additive consisting essentially of a clayey material, the mineral additive includes an amount of crystalline silica which is at most about 15% by weight of the mineral additive, and an inert mineral supplement compatible with the clayey material and dispersible in the plaster board composition.
 2. The plasterboard composition according to claim 1, in which a nature and an amount of the mineral additive are chosen so that the plaster composition contains at most 2% crystalline silica.
 3. The plasterboard composition according to claim 1, in which the nature and the amount of the mineral additive are chosen so that the plasterboard composition contains at most 1% cellular crystalline silica.
 4. The plasterboard composition according to claim 1, in which the mineral additive comprises kaolin, illite, quartz and dolomite.
 5. The plasterboard composition according to the claim 4, in which the mineral additive comprises, in percentages by weight: 25% kaolin; 10% illite; 15% quartz; and 50% dolomite.
 6. The plasterboard composition according to claim 1, in which the unexpanded vermiculite is micronized.
 7. The plasterboard composition according to claim 1, which furthermore includes up to 4% boric acid.
 8. The plasterboard composition according to claim 2, which furthermore includes up to 4% boric acid.
 9. The plasterboard composition according to claim 5, which furthermore includes up to 4% boric acid.
 10. The plasterboard composition according to claim 1, comprising: 70 to 80% of hydratable calcium sulphate; 1% of glass fibres; 10 to 15% of the mineral additive consisting essentially of kaolin, illite, quartz and dolomite; 2 to 4% of micronized unexpanded vermiculite; 6 to 10% of hydrated alumina; and 0 to 2% of boric acid.
 11. A plasterboard consisting essentially of a hardened composition according to claim
 1. 12. A plasterboard consisting essentially of a hardened composition according to claim
 6. 13. A plasterboard consisting essentially of a hardened composition according to claim
 7. 14. A plasterboard consisting essentially of a hardened composition according to claim
 10. 15. A plasterboard consisting essentially of a hardened composition according to claim 1, in which the density is between 800 and 1,000 kg m³.
 16. The plasterboard according to claim 11, in which at least one of its sides is coated with a reinforcing material based on mineral and/or refractory fibres, or based on cardboard.
 17. The plasterboard according to claim 16, in which each of its two sides is coated with a reinforcing material based on glass fibres.
 18. The plasterboard according to claim 12, in which at least one of its sides is coated with a reinforcing material based on mineral and/or refractory fibres, or based on cardboard.
 19. The plasterboard according to claim 18, in which each of its two sides is coated with a reinforcing material based on glass fibres.
 20. The plasterboard according to claim 13, in which at least one of its sides is coated with a reinforcing material based on mineral or refractory fibres, or based on cardboard.
 21. The plasterboard according to claim 20, in which each of its two sides is coated with a reinforcing material based on glass fibres.
 22. The plasterboard according to claim 14, in which at least one of its sides is coated with a reinforcing material based on mineral or refractory fibres, or based on cardboard.
 23. The plasterboard according to claim 22, in which each of its two sides is coated with a reinforcing material based on glass fibres.
 24. A method of preparing a composition according to claim 1, comprising mixing the constituents of the composition together in any order.
 25. A method of preparing a composition according to claim 6, comprising mixing the constituents of the composition together in any order.
 26. A method of preparing a composition according to claim 7, comprising mixing the constituents of the composition together in any order.
 27. A method of preparing a composition according to claim 10, comprising mixing the constituents of the composition together in any order.
 28. A continuous process for manufacturing plasterboards, essentially comprising the following steps: mixing the various constituents of the composition according to claim 1 with water to form a slurry; depositing the slurry on a reinforcing material, followed by shaping and covering an upper face of the slurry using a second reinforcing material; where appropriate, shaping edges of the board by moulding the board on profiled bands; setting the composition on a manufacturing line that runs along a conveyor belt; cutting the set composition at the end of the line into predetermined lengths; and; drying of the boards obtained.
 29. A continuous process for manufacturing plasterboards, essentially comprising the following steps: mixing the various constituents of the composition according to claim 6 with water to form a slurry; depositing the slurry on a reinforcing material, followed by shaping and covering an upper face of the slurry using a second reinforcing material; where appropriate, shaping edges of the board by moulding the board on profiled bands; setting the composition on a manufacturing line that runs along a conveyor belt; cutting the set composition at the end of the line into predetermined lengths; and; drying of the boards obtained.
 30. A continuous process for manufacturing plasterboards, essentially comprising the following steps: mixing the various constituents of the composition according to claim 7 with water to form a slurry; depositing the slurry on a reinforcing material, followed by shaping and covering an upper face of the slurry using a second reinforcing material; where appropriate, shaping edges of the board by moulding the board on profiled bands; setting the composition on a manufacturing line that runs along a conveyor belt; cutting the set composition at the end of the line into predetermined lengths; and; drying of the boards obtained.
 31. A continuous process for manufacturing plasterboards, essentially comprising the following steps: mixing the various constituents of the composition according to claim 10 with water to form a slurry; depositing the slurry on a reinforcing material, followed by shaping and covering an upper face of the slurry using a second reinforcing material; where appropriate, shaping edges of the board by moulding the board on profiled bands; setting the composition on a manufacturing line that runs along a conveyor belt; cutting the set composition at the end of the line into predetermined lengths; and; drying of the boards obtained. 